Polyamides based on dimer fatty acids and diamines are known to be useful as binders in liquid inks, especially for packaging applications. These polyamides show excellent solubility and adhesion to numerous substrates especially plastic films such as polyester, nylon and polyolefins.
German patent DE 1520940 describes polyamides comprising dimerized fatty acids, an unbranched aliphatic monocarboxylic acid with 1 to 5 carbon atoms, ethylenediamine and an unbranched co-diamine with 4 to 10 carbon atoms as binders for printing inks. The purity of the dimerized fatty acid used in the examples varied in the range between 75% and 99%.
German patent DE 1645408 describes polyamides comprising dimerized fatty acids, an unbranched aliphatic monocarboxylic acid with 1 to 5 carbon atoms, ethylenediamine and aromatic or cycloaliphatic co-diamines as binders for printing inks.
U.S. Pat. No. 3,412,115 describes polyamides comprising a dimeric fatty acid, an alkylenediamine having from 2 to 3 carbon atoms, hexanemonocarboxylic acids and optional further monocarboxylic acids as binders for printing inks. The patent discloses (column 3, lines 7 to 13) that typical compositions of commercially available polymeric fatty acids (manufactured by oligomerization of C18 unsaturated fatty acids) is: 5 to 15% monobasic acids, 60 to 80% dibasic acids and 10 to 35% tribasic (and higher) acids. For the purpose of the invention disclosed in U.S. Pat. No. 3,412,115 the monomeric fatty acid content can vary from 1 to 5% as low range and from 15 to 20% as high range.
U.S. Pat. No. 4,571,267 describes polyamides which comprise polymerized fatty acids, at least one unbranched and one branched monocarboxylic acid, ethylenediamine and hexamethylenediamine as binders for printing inks. According to the examples of the patent the commercial dimeric fatty acid which was used to prepare the polyamides had a dimer content of 75%.
U.S. Pat. No. 6,710,121 B2 describes nitrocellulose-compatible laminating ink resins which are prepared by reacting together reactants including polymerized fatty acid, co-diacid, monoacid, secondary diamine and C6-diamine, where the co-diacid comprises 1,4-cyclohexanedicarboxylic acid. The patent discloses (column 3, lines 32ff) that the polymerized fatty acid contains preferably less than 25% of trimer acid and high.order polymerization product and that dimer acid constitute at least about 75% of the polymerized fatty acid, preferably 80-90% dimer fatty acid and in one aspect essentially all of the polymerized fatty acid.
The polyamides of the state of the art based on dimeric fatty acid have in common that the dimer fatty acid content is high, at least 75% and that the amount of monomeric species is low, typically 5 to 15% with a maximum amount for monomeric species of 15 to 20% (see citation of U.S. Pat. No. 3,412,115 above).